Mobile communication devices such as mobile phones, personal data assistants, and the like are generally powered by internal means, such as an internal battery pack. The internal battery pack is an assembly of one or more batteries/cells that typically have a predetermined capacity. Typically, battery packs can have different termination voltages (associated with full charge) such as 4.2 V and 4.4 V, for example, as well as different charging/discharging characteristics.
As is well understood, the battery pack needs to have a sufficient capacity to operate the mobile communication device under a variety of conditions, including handling the comparatively greater power requirements encountered when transmitting a signal wirelessly. In transmitting a wireless signal, a mobile communication device generates an internal data signal that is transmitted using a radio transmitter. The data signal is typically a comparatively low frequency signal that is generally referred to as a baseband signal. The baseband signal is mixed with a carrier signal having a substantially higher frequency to produce a high (e.g. radio) frequency transmission signal. The transmission signal is amplified in one or more stages of an output power amplification block and then applied to a radio antenna to be radiated. The amplified transmission signal needs to be sufficiently powered so that it is received with appropriate strength and little or no data loss at a remote base station or another communication device.
The amplification stages of the output power amplification block may include a pre-amplification stage and a power amplification stage for producing the amplified transmission signal. The amplification level of either the pre-amplification stage or the power amplification stage may generally be adjusted depending on the power required for a particular type of signal. The power amplification stage is powered so that it can produce an amplified transmission signal that has an appropriate instantaneous maximum power for the required transmission.
In wireless communications, there are many cases where the amplified transmission signal is required to have a large dynamic range of power levels. This range is needed in order to accommodate a signal that has a high peak-to-average power ratio (PAPR) or to accommodate different types of signals that may have different desired power levels and different PAPRs. In these cases, the power amplification stage must be capable of generating an amplified transmission signal such that the highest instantaneous power level desired for any data type or data rate of the baseband data that is present in the amplified transmission signal is always accommodated without saturation or undue distortion. In conventional power management schemes, the maximum instantaneous power increases with available power supply voltage, such that insufficient supply voltage may induce amplifier saturation and excessive distortion. As such, the power amplification stage is typically provided with a power supply voltage that is sufficient for accommodating a specified maximum instantaneous power level. For lower power levels, the excess power supplied to the power amplifier is unnecessary and is generally dissipated as heat or otherwise lost.
In wireless devices that are using a battery, the supply current requirements of the amplifier can constitute a heavy drain on the battery. For example, a GSM transmit pulse has a very high current drain on the battery for a time of ˜500 usec and the current can reach ˜2 Amps. Such a pulse causes the voltage appearing at the power amplifer stage (PA) to “slump” because of battery internal source resistance (ISR) and other printed circuit board (PCB) trace/component resistances.
This battery voltage slump has led to standards that require the PA to operate with a minimum voltage requirement. These standards include, for example, FCC regulations as well as GSM standards with regard to radiated emissions. However, it is difficult to accurately choose/set the minimum voltage level of the PA, because battery ISR can have a wide range depending on the age of the battery, the temperature at which the battery is operating and the like. For example, the worst case slump for cold temperatures and an aged battery can be 2-3 times the slump of a newer battery at indoor temperatures. Thus, in order to design a mobile device that is compliant with standards, the worst case slump must be considered and a lower PA operating voltage must generally be assumed in order to meet the “worst case scenario”. The use of a lower PA operating voltage sacrifices efficiency and available power because in conditions where battery slump is better than the worst case, there will be excess power that is dissipated. This results in shorter battery life and lower production yields.
As such, there is a need in the art for an improved method of monitoring and managing battery slump voltage in mobile devices.
These and other features of the exemplary embodiments are described in more detail below.